1. Field of the Invention
The invention relates to a lid for closing a cup along a circumferential sealing rim, where the lid comprises at least one aluminum foil and an optionally multilayer polymer film coextruded on to the aluminum foil and a cohesive line of weakness is provided in the polymer film, corresponding to the preamble of claim 1.
2. Description of Related Art
Such a lid is known, for example, from WO 2008/006123 A, corresponding to AT 009 750 U and EP 2 040 915 A, published in 2008. This document concentrates on the structure of the material layers forming the contact surface on the two sides of the contact surface.
It is known from WO 2007/065055 A, corresponding to EP 1 954 582 A and U.S. Pat. No. 4,693,390, published in 2007, that the two layers can be adhesively bonded to one another; the line of weakness is introduced by means of a laser beam which is not described in more detail.
EP 0 812 782 A, published in 1997, likewise discloses such a lid. Here, the polymer film comprises at least two layers, with the innermost layer having incisions or lines of weakness near the rim which bound oval regions. After sealing onto a filled cup, peeling off the lid results, due to the predetermined adhesion conditions between the individual layers and the strength of the seal at the rim of the cup, in the inner layer of the plastic film remaining firmly sealed to the container rim, the outer layer of the plastic film and the aluminum foil being peeled off and the oval region which is defined by the lines of weakness of the innermost film remaining adhering to the outer layer on peeling off and thus providing an opening suitable for a drinking straw or drinking from the cup.
The creation of the adhesion between the individual films/layers and the lines of weakness is achieved by means of melting processes which are brought about by means of appropriately heated and profiled rollers while the film runs through them. Although this application originating in the year 1996 comes from one of the largest lid manufacturers in Europe, the subject matter of the patent application never came on to the market; it was not possible to produce it in a commercially justifiable time and at commercially justifiable cost.
EP 1 278 630 B discloses a similar lid which is said to be resealable after opening. For this purpose, a pressure-sensitive adhesive is provided in particular regions of the lids. Apart from the resealability, there are various similarities with the first-named document when the lid is made more mechanically stable in the interests of resealability. For opening only once, this lid is too complicated, and in addition it has been found, in this design, that the separation between the layers is unreliable and the inner layer does not reliably remain in the region of the opening.
AT 501 789 B by the applicant is of an earlier date and has the same objectives as the first-named document and likewise attempts to create the lines of weakness by means of a heatable tool in a thermomechanical way. Here too, reliable and commercially justifiable production is not successful.
A document from far back in 1979, viz. DE 29 01 581 A, attempted to provide a solution to peeling off a layer of a multilayer lid on specific cups having a rolled rim so as to form an opening in the remaining lid material, but this product never came on to the market either.
A similarly old document, viz. FR 2 503 036 A, proposes a very similar solution, namely coextrusion of an aluminum foil and a polymer film, the latter being separated from the composite by lines of weakness in the prescribed regions and being taken off by the aluminum when the lid is peeled off in these places, so that a lid having an opening remains at the rim of the cup even after opening.
Even considerably later (1987), the application of the last-named French document protected an improvement in the USA, but none of the products came on to the market despite the large patenting efforts.
A document concerning somewhat different objectives which goes back to 1971 is DE 22 40 234 A, which seals a two-layer covering film to the container rim in dish-shaped packaging for fresh meat, with the outer layer being impermeable to oxygen and the inner layer being permeable to oxygen. As a result of a weakening of the inner layer in the region of a peeling tab, it is possible to peel off the outer layer alone and thus allow the ageing process for the meat to commence. This packaging was not able to become established, if it appeared on the market at all.
A recent, once again generic, document is WO 2007/088426 A, which contains a series of variants of the documents discussed above (in particular the first-named document). It is notable here that the treatises are extremely cursory so that they actually put forward only ideas but not actually functional solutions. This can be seen in a comparison of FIG. 4 with the associated description, since FIG. 4 is supposed to represent the case in which the outer side of the lid has the lines of weakness, but this means that the hatched part having the reference numeral 24 cannot assume the position shown on being peeled off, because it is the outermost layer which is separated off.
It is stated elsewhere in the text that the lines of weakness can also be provided on the innermost layer or, when more than two films/layers are present, also at the intermediate layers. How this is supposed to function either in production or on opening is not indicated in more detail.
For the production of the lines of weakness, too, mention is merely made of all conceivable possibilities without even one of these being described in detail. It is merely said quite succinctly that a stamping tool or the like or a laser beam can be used. This document is, as mentioned above, of relatively recent date (priority Feb. 2, 2006) and no product corresponding to the content of this document has yet appeared on the market; it would hardly be possible to manufacture such a product on an industrial scale on the basis of the information given in the patent application.
Conventional lids which are sealed to a cup along a circumferential sealing rim for full-area opening suffer from problems that the sealing strengths actually achieved are time and time again too great for normal opening and tearing of the lid, spillage of the contents of the cup because of the great amount of force which has to be applied and similar unpleasant effects therefore occur. The reason is that the packaging companies at which sealing is carried out pay attention mainly to the seal being impermeable and, in the event of problems which are sometimes attributable to a dirty tool, poorly aligned lid feed, etc., tend simply to alter the parameters for the sealing strength (temperature, pressure, time) on the sealing machine so that the desired impermeability of the seal is obtained in each case. However, this virtually inevitably leads to the abovementioned overstrong bonding regions being created at individual places along the sealing seam, which present the user with the abovementioned unacceptable problems. It is an object of an embodiment of the invention to solve this problem.